support for multi-values attribute in Component Matching

- only for equality matching
- only components of ASN.1 types used in an X.509 certificate can be indexed
(composite types except for RDN and DN are not supported yet)
- how to use
index [attribute name].[component reference] eq
Ex)
index userCertificate eq
index userCertificate.toBeSigned.issuer.rdnSequence eq
index userCertificate.toBeSigned.serialNumber eq
index userCertificate.toBeSigned.version eq

2) attribute aliasing support
- x509CertificateIssuer
- x509CertificateSerial
- x509CertificateIssuerAndIssuer
3) AuthorityKeyIdentifier support(one of certificate extension)
4) Misc. improvement
- integrate OID and its decoder mapping table
- normalize and validate the values of both component asserions and
  extracted components
5) Misc. bug fix

2) remove double buffering for decoded component values
3) caching decoded component assertion values

2) nibble type memory support when decoding
3) description type object identifier support
4) OPTIONAL, DEFAULT support in certificate decoder/extractor/matching
5) Misc bug fix

See "contrib/slapd-modules/comp_match/README" to understand
what's the purpose of  this patch is and how to use it.